Method for producing a metal part

ABSTRACT

The invention relates to methods of casting metal parts in sand molds, with the particularity that it is not necessary to use sleeves surrounding the feed risers which are arranged outside the part to offset the shrinkage occurring during the solidification of the molten metals. The operations of placing the sleeves which must be arranged around the risers are eliminated with the method object of the invention, the actual sleeves being made when the sand mold is produced.

TECHNICAL FIELD OF THE INVENTION

The invention is comprised among the methods of casting metal parts insand molds, and it specifically relates to a method which allowssupplying insulating and/or exothermic material in areas of the sandmold which will be in contact with the molten metal and in which agreater insulation or heat supply is required.

BACKGROUND OF THE INVENTION

The production of cast metal parts comprises pouring a molten metal intoa mold, the solidification of the metal and demolding of the part formedby means of eliminating or destroying the mold.

When molten metal is poured into a mold and left to solidify, the metalshrinks during its solidification and its volume is reduced. To offsetthis shrinkage and to assure the production of quality molded parts, itis usually necessary to use so-called feed risers located outside thepart. When the molded part solidifies and shrinks, feeding molten metalfrom the riser to the part prevents the formation of shrinkage cavities.

Two casting boxes (of wood, steel, etc.) are generally used to produce asand mold, in each of which a half mold is produced with a specificportion of the cavity which, when the two half sand molds are joined,will determine the cavity with the shape of the part to be produced.

A casting box in which the portion of the corresponding model is placedis used to produce each half sand mold, the rest being filled with amixture of agglomerated sand and its catalyst.

Joining the half sand molds by the faces presenting the cavity leads tothe sand mold with the cavity that is to be filled with molten metal toshape the metal part.

As discussed above, the volume of molten metals is reduced duringsolidification. For this reason, when casting metals it is common to userisers arranged outside the part to offset the shrinkage which occursduring solidification. To improve the feed effect and in order for thevolume of the feed riser to be kept at a minimum, the feed riser isnormally surrounded with an exothermic and/or thermal insulating sleevefor the purpose of keeping the metal of the riser in the molten statefor the longest possible time.

These sleeves are placed before performing the casting operations in asupport firmly fixed to the model. After making the mold, the support isremoved in order to produce a feed cavity, i.e., the riser surrounded bythe sleeve. When the molten metal is introduced through the castingchannel or sprue, the metal flows through it, filling on one hand thecavity of the mold which will shape the molded part and, on the otherhand, the feed riser. Since the riser is surrounded by the exothermicand/or insulating sleeve, the metal will be in a liquid state for alonger time period as it solidifies and the metal shrinks in the rest ofthe part, thus allowing the feed of the molten metal to offset theshrinkage and thus reduce the formation of shrinkage cavities to aminimum.

Depending on the geometry of the part to be produced, the mold will needmore or less risers, and each of them will be surrounded by anexothermic and/or insulating sleeve. Therefore, before pouring themolten metal into the mold, the sleeves will have had to have beenplaced in their respective risers, considerably increasing the workcycle.

As previously indicated, the risering areas are defined in the sand moldby the model itself in which, in addition to the geometry of the part tobe produced, the risering areas outside the part are shaped. Theserisering areas must be covered before casting with the correspondinginsulating and/or exothermic sleeves.

When the part presents constrained areas or difficult to feed areas thatdo not allow feeding the rest of the part before it solidifies, thetechnique referred to as padding is typically used, which consists ofproducing in the sand mold a flaring of the constrained area or the areawhich is difficult for the liquid metal to access, in order to producean excess of metal which assures complete filling of that area of thecavity. This solution which solves the problem of a suitable casting ofthe part has the drawback that it is later necessary to eliminate thepadding, which involves an expensive deburring operation.

Until now, the operation of placing the sleeves around the risers hasbeen an essential operation; it would therefore be desirable to be ableto do away with this operation by making the sleeves when the sand moldis produced.

On the other hand, the foundryman generally manufactures the sand moldsand the sleeves come from a manufacturer that specializes in sleeves,such that the foundryman does not control the materials and thecomposition of the sleeves, which involves certain risks because thereis a series of materials that are frequently used today in manufacturingsleeves, the use of which under current European laws is restrictedbecause during handling or after casting they can produce emissions orparticles that are hazardous to the health.

However, there materials for manufacturing sleeves with proven use thathave shown their efficiency both at the level of complying with theexpectations required in terms of insulation and exothermic properties,and in that they can furthermore be supplied to the foundry so that thelatter can, “in situ”, produce the sleeves and the risering areasrequired for the manufacture of the part. Sleeves of these features aredescribed in patents EP 1543897 and EP 0265112. It would therefore bedesirable to be able to supply insulating and/or exothermic materialswhen manufacturing the sand mold in those areas in which a greaterinsulation or heat supply is required.

DESCRIPTION OF THE INVENTION

The object of the invention is a method of producing metal parts bycasting a molten metal into a sand mold which allows applying aninsulating or exothermic material in areas of the mold which require agreater insulation or heat supply by exothermic reaction, such asrisering areas or internal areas of the mold and all this during aprocess of manufacturing the sand mold. This allows, “in situ”, makingthe sleeves which are to surround the risers and supplying insulating orexothermic material in areas which are difficult to feed that do notallow feeding the rest of the part before it solidifies.

To that end, the method object of the invention comprises the followingsteps:

-   -   a) placing, in a casting box, a model for shaping a cavity which        will define the shape of the metal part and at least one riser,    -   b) pouring a molding sand into the casting box after step a),    -   c) pouring an insulating or exothermic mixture into the casting        box after step a) to delay the solidification of a molten metal,    -   d) extracting the model for shaping the mentioned cavity,    -   e) casting a molten metal into the mentioned cavity,    -   f) extracting the part produced after the solidification of the        molten metal.

The insulating or exothermic mixture is arranged in contact with themodel in some areas in which it is required that the molten metal castin step e) remains in the liquid state for a longer time period than therest of the molten metal that is going to shape the part, such that,once the model is removed in step d), the insulating or exothermicmixture delays the solidification of the molten metal cast in step e) inthe areas in which the mentioned mixture has been arranged.

The choice of an insulating or exothermic mixture will depend on thethermal characteristics of the metal which is going to be melted, on thedimensions of the part, on its geometry and on other variants, forexample, if the part is a non-ferritic metal part with low meltingpoint, the mixture used could be an insulating mixture.

If the model placed in the casting box has any area which is difficultto feed or a constrained area which makes it difficult to feed anotherarea of the part with molten metal, the insulating or exothermic mixturewill be deposited in contact with the model in that constrained areabefore pouring the molding sand so that when casting the molten metal,said metal in the mentioned constrained area will remain in the liquidstate for a longer time period than the rest of the metal that is goingto shape the part and can therefore feed other areas.

However, if the area in which the insulating or exothermic mixture isgoing to be deposited corresponds, for example, to a riser, an auxiliarypart can be placed around the mentioned riser such that after pouringthe molding sand, the mentioned auxiliary part is removed, a gap beingshaped between the molding sand and the model, into which the insulatingor exothermic mixture forming the sleeve once it is cured will bepoured.

The auxiliary part used for surrounding the riser can be a bush with acircular section which must be able to be extracted, i.e., separatedfrom the riser easily in order to form the aforementioned gap.

The insulating or exothermic mixture can be a non-fibrous mixture, suchas those described in patents EP 1543897 and EP 0265112, such that themolding sand and the mentioned insulating or exothermic mixtures whichwill shape the mold can be located in independent tanks. These inputmaterials fall into a hopper and from there into a continuous or batchmixer in which they will be mixed with the corresponding resins andcatalysts coming from other tanks. The molding sand along with theresins and catalysts are poured into the casting box. The insulating orexothermic materials which are already mixed with the resins andcatalysts are also poured into the casting box in the locationcorresponding to them.

DESCRIPTION OF THE DRAWINGS

To complete the description and for the purpose of aiding to betterunderstand the features of the invention according to a preferredembodiment thereof, a net of drawings is attached as in integral part ofsaid description, in which the following has been depicted with anillustrative and non-limiting character:

FIG. 1 shows a sectional view of the upper casting box in which thecorresponding model and the riser, along with the casting channel havebeen placed.

FIG. 2 shows a sectional view of the upper casting box in which aninsulating or exothermic mixture has been deposited in an area withdifficult access for the molten metal to reach it. Furthermore, it isalso observed in this figure that an auxiliary part has been arrangedaround the riser.

FIG. 3 shows a sectional view of the upper casting box in which themolding sand completely filling the box has been poured.

FIG. 4 shows a sectional view of the upper casting box once theauxiliary part surrounding the riser and shaping a gap has been removed.

FIG. 5 shows a sectional view of the upper casting box with the gapfilled with the insulating or exothermic mixture.

FIG. 6 shows a sectional view of the upper casting box in the moment inwhich the extraction of the model and of the casting channel begins.

FIG. 7 shows a sectional view of the upper portion of sand mold once themodel and the casting channel have been completely removed from theupper casting box.

FIG. 8 shows a sectional view of the complete sand mold, i.e., its upperand lower portions, in which the cavity which is going to shape the parthas been filled with the molten metal supplied from the casting channel.

FIG. 9 shows a schematic view of an installation comprising the materialtanks, dispenser, mixer and other components of the installation.

PREFERRED EMBODIMENT OF THE INVENTION

FIG. 1 shows a casting box (3), namely the upper box, inside which amodel (4) has been arranged for shaping a cavity (5), which will definethe shape of the metal part (1), and at least one riser (11).Furthermore, the corresponding model for shaping the casting channel orsprue (10) also has been placed in this upper casting box (3).

Though it is not depicted in the drawings, for shaping the sand mold (2)it is also necessary to have a lower casting box (3) in which thecorresponding model for defining another cavity will be placed which,when joined with the cavity defined by the model placed in the uppercasting box (3), will shape the cavity corresponding with the part to beproduced and which will be filled with molten metal. As previouslyindicated, first a model is placed in a lower box and molding sand ispoured in order to subsequently overturn the lower box and placethereupon the upper box with another model and the feed channels alreadyarranged.

FIG. 1 shows areas (41, 42) which, due to their configuration, are areasin which it is required that the metal which will be cast in the cavity(5) remains in the liquid state for a longer time period than the restof the metal which is going to shape the part (1).

In this case, the area (41) corresponds to a riser (11) which will beformed once the molten metal is cast, and the area (42) is an area withdifficult access for the molten metal to reach it. The risers are usedto offset the shrinkage occurring during the solidification of themetals, such that feeding molten metal from the riser (11) into thecavity (5) allows the complete filling thereof and thus the productionof quality parts. To improve feeding from the riser (11) and in orderfor the molten metal to reach areas with difficult access, such as thearea (42) for example, the method object of the invention allowssupplying an insulating or exothermic mixture (7) in contact with themodel (4) in the areas (41, 42) so that the molten metal cast into thecavity (5) remains in the liquid state in the areas (41, 42) for alonger time period than the rest of the metal which will shape the part(1).

FIG. 2 shows that in the area (42), which is an area that is difficultto feed that does not allow feeding the rest of the part, there has beendeposited the insulating or exothermic mixture (7), which allowsdelaying the solidification of the metal cast in that the area (42).This mixture (7) will be arranged in the area (42) before pouring themolding sand (6) into the casting box (3). It can also be seen in thisFIG. 2 that in the area (41), which will form the riser (11), anauxiliary part (8) has been placed around the same, in this case theauxiliary part (8) being a bush with a circular section due to the shapeof the riser.

Once the bush is placed around the area (41) and the insulating orexothermic mixture (7) has been poured, the molding sand (6) is pouredas can be seen in FIG. 3.

As is shown in FIG. 4, after pouring the molding sand (6) into thecasting box (3), the bush is extracted such that a gap (9) is createdbetween the molding sand (6) and the area (41). As is shown in FIG. 5,the gap (9) is filled with the insulating or exothermic mixture (7) inorder to allow that the solidification of the molten metal in the area(41) once it is cast in the cavity (5) is delayed.

In FIG. 6, the model (4), along with the model shaping the castingchannel or sprue (10), are being removed in order to define the cavity(5) which will be filled with molten metal cast through the castingchannel (10), as shown in FIG. 8. The complete extraction of the model(4) and of the model shaping the sprue (10) is shown in FIG. 7. When themodels, the casting box (3) are removed and the molding sand is cured,the upper portion of the sand mold (2), the cavity (5) of which will befilled with molten metal, is produced.

The steps described above will be applied to a lower casting box (2),with the exception that it is not necessary to arrange the castingchannels in the lower casting box (3), it is simply necessary to placethe corresponding model for shaping a cavity which, along with thecavity produced in the upper casting box (3), will shape a cavity thatwill be filled with molten metal for shaping the metal part.

FIG. 8 shows the complete sand mold (2), with the upper and lowerportions, in which there has been defined a cavity corresponding withthe final shape of the metal part (1) to be produced. The cavity of thesand mold (2) has been filled with molten metal through the sprue (10).In the areas (41, 42) in which the insulating or exothermic mixture (7)has been deposited, the molten metal will remain in the liquid state fora longer time period than the rest of the metal in order to completelyfill the entire cavity and in order for the metal to reach areas whichare difficult to feed, such as the area (42), for example.

Though it has not been depicted in the drawings, once the molten metalhas solidified, the sand mold (2) is destroyed to extract the metal part(1). Once extracted, it will be necessary to remove the riser (11) andthe sprue (10) by any of the methods known in the industry.

Areas (41, 42) in which it is required that the molten metal remains inthe liquid state for more time have been produced in the moment ofshaping the sand mold (2) with the method object of the invention.

FIG. 9 schematically shows an industrial installation for producingmetal parts according to the invention. The installation depicted hasthree tanks (12) or hoppers with the materials involved in the process.Thus, for example, the sand for shaping the sand mold (2) is in one ofthese tanks (12), the insulating mixture is in another tank (12) and theexothermic mixture is in another one.

The suitable amount is dispensed from each tank (12) into a distributionhopper (14) which pours it into a mixer (13). The resins and thecatalysts coming from the tanks (15) enter the continuous or batch mixer(13). Once the mixtures, whether the mixed molding sand (6) or the mixedinsulating or exothermic mixture (7), are produced, they are depositedby gravity in the casting boxes (3) in the location corresponding tothem.

1. A method of producing a metal part (1) by casting a molten metal intoa sand mold (2), characterized in that it comprises: a) placing a model(4) in a casting box (3) for shaping a cavity (5) which will define theshape of the metal part (1) and at least one riser (11), b) pouring amolding sand (6) into the casting box (3) after step a) for shaping thesand mold (2), c) pouring an insulating or exothermic mixture (7) intothe casting box (3) after step a) to delay the solidification of amolten metal, d) extracting the model (4) for shaping the mentionedcavity (5), e) casting a molten metal into the mentioned cavity (5), f)extracting the part (1) produced after the solidification of the moltenmetal, wherein the insulating or exothermic mixture (7) is arranged incontact with the model (4) in some areas (41, 42) in which it isrequired that the molten metal cast in step e) remains in the liquidstate for a longer time period than the rest of the molten metal that isgoing to shape the part (1), such that once the model (4) is removed instep d), the insulating or exothermic mixture (7) delays thesolidification of the molten metal cast in step e) in the areas (41, 42)in which the mentioned mixture (7) has been arranged.
 2. The method ofproducing a metal part (1) according to claim 1, further comprising,after step a), placing an auxiliary part (8) around the area (41), suchthat after step b) the mentioned auxiliary part (8) is removed, a gap(9) being shaped between the molding sand (6) and the model (4), intowhich the insulating or exothermic mixture (7) of step c) is poured. 3.The method of producing a metal part (1) according to claim 2, whereinthe auxiliary part (8) is a bush with a circular section.
 4. The methodof producing a metal part (1) according to claim 1, wherein theinsulating or exothermic mixture (7) is a non-fibrous mixture.
 5. Themethod of producing a metal part (1) according to claim 1, wherein theinsulating or exothermic mixture (7) is in contact with the molten metalin an area (41) forming the riser (11) to supply heat or insulation. 6.The method of producing a metal part (1) according to claim 1, furthercomprising arranging the insulating or exothermic mixture (7) in contactwith a portion of the molten metal in an area with difficult access (42)of the part (1) which requires a heat supply or insulation.
 7. Themethod of producing a metal part according to claim 1, wherein themolding sand (6) and the insulating or exothermic mixture (7) shapingthe sand mold (2) are located in independent tanks (12) feeding a mixer(13) in which they are mixed with agglomerating resins so that theyaccess the casting box (3) by gravity.
 8. The method of producing ametal part (1) according to claim 2, wherein the insulating orexothermic mixture (7) is a non-fibrous mixture.
 9. The method ofproducing a metal part (1) according to claim 3, wherein the insulatingor exothermic mixture (7) is a non-fibrous mixture.
 10. The method ofproducing a metal part (1) according to claim 2, wherein the insulatingor exothermic mixture (7) is in contact with the molten metal in an area(41) forming the riser (11) to supply heat or insulation.
 11. The methodof producing a metal part (1) according to claim 3, wherein theinsulating or exothermic mixture (7) is in contact with the molten metalin an area (41) forming the riser (11) to supply heat or insulation. 12.The method of producing a metal part (1) according to claim 4, whereinthe insulating or exothermic mixture (7) is in contact with the moltenmetal in an area (41) forming the riser (11) to supply heat orinsulation.
 13. The method of producing a metal part (1) according toclaim 9, wherein the insulating or exothermic mixture (7) is in contactwith the molten metal in an area (41) forming the riser (11) to supplyheat or insulation.
 14. The method of producing a metal part (1)according to claim 2, further comprising arranging the insulating orexothermic mixture (7) in contact with a portion of the molten metal inan area with difficult access (42) of the part (1) which requires a heatsupply or insulation.
 15. The method of producing a metal part (1)according to claim 3, further comprising arranging the insulating orexothermic mixture (7) in contact with a portion of the molten metal inan area with difficult access (42) of the part (1) which requires a heatsupply or insulation.
 16. The method of producing a metal part (1)according to claim 4, further comprising arranging the insulating orexothermic mixture (7) in contact with a portion of the molten metal inan area with difficult access (42) of the part (1) which requires a heatsupply or insulation.
 17. The method of producing a metal part (1)according to claim 13, further comprising arranging the insulating orexothermic mixture (7) in contact with a portion of the molten metal inan area with difficult access (42) of the part (1) which requires a heatsupply or insulation.
 18. The method of producing a metal part accordingto claim 2, wherein the molding sand (6) and the insulating orexothermic mixture (7) shaping the sand mold (2) are located inindependent tanks (12) feeding a mixer (13) in which they are mixed withagglomerating resins so that they access the casting box (3) by gravity.19. The method of producing a metal part according to claim 3, whereinthe molding sand (6) and the insulating or exothermic mixture (7)shaping the sand mold (2) are located in independent tanks (12) feedinga mixer (13) in which they are mixed with agglomerating resins so thatthey access the casting box (3) by gravity.
 20. The method of producinga metal part according to claim 17, wherein the molding sand (6) and theinsulating or exothermic mixture (7) shaping the sand mold (2) arelocated in independent tanks (12) feeding a mixer (13) in which they aremixed with agglomerating resins so that they access the casting box (3)by gravity.